In an effort to maximize the service life and integrity of a pipeline, the pipeline is commonly coated with a protective coating which provides a primary corrosion barrier and reduces the ravages of corrosion. In the past, pipelines have been coated with coal tar enamel, asphalt or tape coatings. More recently, plural-component epoxy-like coatings have been developed for coating.
The coating of a new pipeline, or the cleaning and recoating of an existing pipeline are expensive undertakings. Over the years, many devices have been developed which actually travel along a section of the pipeline to perform part of the operation. For example, line travel devices have been developed which brush a preexisting line, remove existing coatings using high pressure water jets and prepare the surface of the line using mechanical blast and air abrasive blast machines. Line travel devices also exist which apply a cold applied tape coating, apply a coal tar enamel or apply a plural component coating system. Many of these devices perform more than one operation to the pipeline as it moves along.
Whether the pipeline is being built for the first time, or the line has been dug up out of the ground, the pipeline is laid on the ground for preparation or rehabilitation. In each of these instances, the pipeline will consist of many joints of pipe, usually welded together into a section. The pipeline sections may be as short as 200 feet and up to a mile long, depending on right of way and other considerations. Each section of the pipeline must undergo all operations done by the line travel equipment.
After completing the operation on one pipeline section, the line travel device must be taken off the section and placed onto the next pipeline section to begin work. This is a complicated and time consuming operation resulting in considerable nonproductive time. Line travel devices normally require two side booms for operation. One side boom, called a cradling side boom, is used to lift the pipeline section ahead of the line travel device. This side boom uses a cradle to support the line and holds the line travel device upright. A second side boom is referred to as a catch-off side boom and is used, among other things, to hold the pipeline when taking the line travel device off the line and installing it on the new section.
The process of getting on and off a pipeline section includes the following steps:
1. The cradling side boom holding the cradle will continue to the end of the pipeline section, bringing the cradles as near to the end of the pipeline section as is safe.
2. The line travel device will travel up to the cradles and then stop whatever operation is being done.
3. The catch-off side boom will come behind the line travel device and hold up the pipeline section using a belt or sling.
4. The cradling side boom will lower the pipeline section until the entire pipeline section weight is supported by the catch-off side boom.
5. The cradling side boom will then pull ahead and drop the cradles on the ground. If the cradles are being used in a surface preparation or coating application, the cradle must be placed on a tarp to prevent them from becoming dirty.
6. The cradling side boom then backs up and attaches directly to the line travel device.
7. The line travel device resumes operation and the cradling side boom "walks" the device off the end of the pipeline section.
8. The catch-off side boom lowers the pipeline section to the pipe supports and removes the belt or sling.
9. The catch-off side boom comes around in front of the cradling side boom and picks up the cradles taken off the line earlier.
10. The catch-off side boom then installs the cradles on the next section of pipeline and moves ahead.
11. The catch-off side boom raises the new section of pipeline using a belt or sling.
12. The cradling side boom then installs the line travel device on the new section of pipeline.
13. The cradling side boom disconnects from the line travel device and pulls ahead and connects to the cradles.
14. The cradling side boom lifts the pipeline section and backs up into position within the guides or stinger of the line travel device.
Only after all these steps have been completed is the line travel device ready to begin operation on the new pipeline section.
This procedure has inherent problems, among which are the following:
1. It is very time consuming, frequently requiring between 40-60 minutes depending upon terrain. The average pipeline construction or rehabilitation project will have three to five different sections per mile. This equates to as much as five hours of nonproductive time each mile just in removing the line travel device from one section and putting it on the next section.
2. The stopping and restarting of the line travel device at the end of the line frequently results in a poorer quality of service performed on the last 30-40 feet of the line.
3. The line travel service performed while the cradling side boom is walking the unit off the end of the pipeline section is poorer because the travel rate is dictated by the speed of the side boom, not the internal drive components of the line travel device.
4. The line travel device is subject to damage while it is being taken off the pipeline section and installed on the new pipeline section.
5. Taking the line travel device on and off the pipeline section poses a danger to personnel in the area. The line travel devices are often very heavy, weighing as much as 21,000 pounds. The line travel devices are subject to swinging and rotating when they are being moved from one section to another. Personnel are required to steady the equipment and guide it on to the new section, a dangerous operation.
As can be clearly seen, an improved apparatus and method for transferring a line travel device from one pipeline section to another is needed. Ideally, the apparatus and method would reduce the time required to perform this operation while minimizing the possibility of damage to the equipment or harm to the personnel operating it.